The mechanisms behind the alteration of chemical carcinogenesis by the dietary lipotropes, choline, methionine, folic acid and vitamin B-12 have been studied. The metabolism and carcinogenic activity of ethionine in different species is being compared. The levels of S-adenosylmethionine in the livers of animals treated with hepatocarcinogens and liver tumor promoters are being determined. The effects of methylase inhibiotrs on the methylation of macromolecules, on cell transformation in vitro and on carcinogenesis in vivo are determined.